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Non-Target Insects Probably Affected More by Insecticides than by Bt
Crops / November 24, 2008 / News from the USDA Agricultural Research Service

New studies show that non-target insects are
probably affected more by conventional insecticides than by modified crops,
such as corn, that have added genes from the soil bacterium Bacillus
thuringiensis. Click the image for more information about it.

Non-Target Insects Probably Affected More by
Insecticides than by Bt Crops

Non-target insects are probably
affected more by conventional insecticides than by crops that contain genes
from the soil bacterium Bacillus thuringiensis (Bt), according to the
findings of a study by Agricultural Research
Service (ARS) scientists and cooperators. The findings were published
recently in Public Library of
Science ONE.

Bt crops such as maize and cotton are genetically engineered to produce
insect-specific toxins. They target specific insect pests, but the researchers
wanted to determine how these crops influence non-target insects in the
environment.

The scientists compared the abundance of groups of non-target insects. They
first compared the abundance of these insects in Bt crops and non-Bt crops
without any insecticides. They also compared the insect populations in both
types of crops treated with insecticides. And they compared the non-target
insect populations in Bt crops without insecticides versus the populations in
non-Bt crops treated with insecticides.

They formed these groups of non-target insects with data drawn from a
modified version of a public database created by Santa Clara University biologist Michelle
Marvier and colleagues. The toxins examined included Cry1Ab and Cry3Bb in
maize, Cry3A in potato and Cry1Ac and Cry1Ab in cotton.

The researchers observed considerable variability in the effects of Bt
cotton and maize crops on non-target insects. However, the data within the
groups were fairly consistent. The most influential factor was the insecticide
applied. Collectively, insecticides such as pyrethroids, organophosphates,
carbamates and neonicotinoids had larger negative impacts on non-target insects
than did the Bt crops.

The researchers concluded that when it comes to killing non-target insects,
no treatment at all has the least impact. Bt crops have considerably less
impact on non-target insects than do conventional insecticides. Also,
insecticides affect insect populations uniformly, regardless of whether they're
in Bt or non-Bt crop fields.